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([2600:1700:dfe0:49f0:4c4a:ea4e:c31a:9352]) by smtp.gmail.com with ESMTPSA id p5sm5151652qkj.35.2021.03.19.10.43.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 19 Mar 2021 10:43:27 -0700 (PDT) Subject: Re: [PATCH] ARM: Qualify enabling of swiotlb_init() To: Christoph Hellwig Cc: linux-arm-kernel@lists.infradead.org, Konrad Rzeszutek Wilk , Marek Szyprowski , Robin Murphy , "open list:SWIOTLB SUBSYSTEM" , open list , Russell King , Mike Rapoport , Andrew Morton , Ard Biesheuvel , Max Filippov , Catalin Marinas , opendmb@gmail.com References: <20210319040333.183827-1-f.fainelli@gmail.com> <20210319130731.GB2624@lst.de> From: Florian Fainelli Message-ID: Date: Fri, 19 Mar 2021 10:43:22 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210319130731.GB2624@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/19/2021 6:07 AM, Christoph Hellwig wrote: > On Thu, Mar 18, 2021 at 09:03:33PM -0700, Florian Fainelli wrote: >> #ifdef CONFIG_ARM_LPAE >> + if (swiotlb_force == SWIOTLB_FORCE || >> + max_pfn > arm_dma_pfn_limit) > > Does arm_dma_pfn_limit do the right thing even with the weirdest > remapping ranges? Maybe a commen here would be useful. It gets assigned to either 0xffffffff or PHYS_OFFSET + arm_dma_zone_size - 1 which is obtained from the machine descriptor, so I expect it to do the right thing, it works for a Pi 4 in 32-bit mode for instance. This is conditional upon enabling CONFIG_ZONE_DMA for ARM, and will otherwise keep its original value of 0, so this should be safe AFAICT. > >> + swiotlb_init(1); >> + else >> + swiotlb_force = SWIOTLB_NO_FORCE; > > Konrad: what do you think of setting swiotlb_force to SWIOTLB_NO_FORCE > and only switching it to SWIOTLB_NORMAL when swiotlb_init* is called? > That kind makes more sense than forcing the callers to do it. > > While we're at it, I think swiotlb_force should probably be renamed to > swiotlb_mode or somethng like that. Agreed. -- Florian